Cleansing compositions must satisfy a number of criteria including cleansing power, foaming properties, and mildness/low irritancy with respect to the skin, hair and the occular mucosae.
Skin is made up of several layers of cells which coat and protect the keratin and collagen fibrous proteins that form the skeleton of its structure. The outermost of these layers, referred to as the stratum corneum, is known to be composed of 250 .ANG. diameter protein bundles surrounded by 80 .ANG. thick bilayers of epidermal lipids and water. Anionic surfactants can penetrate the stratum corneum membrane and, by delipidization (i.e. removal of the lipids from the stratum corneum), destroy its integrity. This destruction of the stratum corneum bilayers can lead to dry rough skin and may eventually permit the surfactant to interact with the viable epidermis, creating irritation.
Ideal cosmetic cleansers should cleanse the skin gently, causing little or no irritation without defatting and or drying the skin and without leaving skin taut after frequent use. Most lathering soaps, liquids and bars fail in this respect. Also, most current cleansing products do not deliver an adequate moisturizing benefit during cleansing. Therefore, users typically must moisturize their skin in a separate step following cleansing.
Certain synthetic surfactants are known to be mild. However, a major drawback of most mild synthetic surfactant systems, when formulated for skin cleansing, is poor lather performance compared to the highest bar soap standards (bars which are rich in coconut soap and superfatted). On the other hand, the use of known high sudsing anionic surfactants with lather boosters can yield acceptable lather volume and quality. Unfortunately, however, the highest sudsing anionic surfactants are, in fact, poor in clinical skin mildness. Surfactants that are among the mildest, such as sodium lauryl glyceryl ether sulfonate, (AGS), are marginal in lather. These two facts make the balancing of the surfactant selection and the lather and skin feel benefit a delicate process. Rather stringent requirements for cosmetic cleansers limit the choice of surface-active agents, and final formulations represent some degree of compromise. Mildness is often obtained at the expense of effective cleansing, or lathering may be sacrificed for either mildness, product stability, or both.
Furthermore, it would be highly desirable to also deliver skin moisturizers from cleansing compositions, because this would provide users with the convenience of obtaining both a cleansing and a moisturizing benefit from a single product. However, such dual cleansing and moisturizing compositions are difficult to formulate because the cleansing ingredients, in general, tend to be incompatible with the moisturizing ingredients.
Thus a need exists for cleansing compositions which will produce a foam which is abundant, stable and of high quality (compactness), which are effective skin cleansers, which are very mild to the skin and occular mucosae, and which can also deliver a moisturizing agent to the skin. These combined skin cleansing and moisturizing compositions would be termed two-in-one cleansers because of the dual cleansing and moisturizing benefits they would provide.
One highly successful solution to this dilemma of delivering both a cleansing and conditioning benefit from the same product has been in the shampoo area. Two-in-one conditioning shampoos have been developed which deliver suspended silicone hair conditioning agents in the presence of various cleansing surfactants. See U.S. Pat. Nos. 4,788,006, to Bolich, Jr. et al., issued Nov. 29, 1988; 4,741,855, to Grote et al, issued May 3, 1988; and 4,704,272, to Oh et al., issued Nov. 3, 1987. Shampoos, though, generally contain higher levels of more potent surfactants than are needed or desirable for gently cleansing the skin, because the hair has a larger surface area compared to the skin and tends to become soiled with higher levels of sebum, dirt, and other debris. Conversely, the hair generally requires much lower levels of conditioners than the skin, because the hair is easily overconditioned resulting in limp, unmanageable, and resoiled hair. Thus, it is seen that cleansing and moisturizing the skin is different from cleansing and conditioning the hair. Therefore, it would be highly desirable to develop effective, yet gentle, skin cleansing compositions which would also provide a skin moisturizing benefit.
It is therefore an object of the present invention to provide improved personal cleansing compositions which thoroughly cleanse the skin and which also moisturize the skin, i.e. to provide combined skin cleansing and moisturizing compositions.
It is a further object of the present invention to provide combined cleansing and moisturizing compositions which are very mild to the skin and occular mucosae.
It is an even further object of the present invention to provide combined cleansing and moisturizing compositions which will produce a foam which is abundant, stable, and of high quality.
It is a still further object of the present invention to provide methods for cleansing and moisturizing the skin.
It is a yet further object of the present invention to provide methods for delivering combined cleansing and moisturizing compositions as foams.
These and other objects will become readily apparent from the detailed description which follows.